This invention relates to disk drives in general and more particularly to a baffle assembly which reduces air turbulence at the outer disk edge of a disk drive thereby reducing the off-track error produced when positioning a head slider assembly over a magnetic disk for reading and writing information on concentric data tracks located thereon.
With the advent of magnetic disks having higher track densities, e.g., densities over 1500 tracks per radial inch (tpi) and positioning arms of decreased weight and therefore reduced stiffness, the problem of accurate positioning of the transducer head over a data track becomes more acute. Off-track errors on the order of 40 micro inches which were acceptable on prior low density disks are no longer tolerable for positioning a transducer head over a disk having a high track density.
In disk drives, it is common for the head slider assembly to be supported on a short suspension arm mounted on a positioning arm which is aligned with the horizontal. The suspension arm typically is mounted at a small angle with respect to the positioning arm. Applicants have discovered that air turbulence causes such a positioning arm, in particular, upon which a head slider assembly is mounted to undergo vibrations. These vibrations result in corresponding changes in horizontal head position thereby producing undesirable cross track motion of the head. At high track densities even a small change in the horizontal position of the transducer head (e.g., 40 micro inches) produces significant off-track errors.
The problem can best be seen with reference to FIGS. 1-2 of the drawings. FIG. 1 depicts an elevational end view of a disks 10 and 11 and positioning arms 40, 41 and 42. The disks 10 and 11 may be part of a plurality of disks mounted on a spindle (not shown) having a longitudinal axis shown in FIG. 1 at I--I. The disks 10, 11 are mounted in axially spaced horizontal planes which are perpendicular to the longitudinal axis of the spindle. The positioning arms 40, 41 and 42 are mounted in respective horizontal planes on a rotary actuator 30 (not shown in FIG. 1) having a longitudinal axis II--II. At the end of each positioning arm is a transducer head slider suspension assembly comprising a small suspension arm 40a, 41a, 41b and 42a (approximately 1 inch in length) upon which one or more heads, schematically shown at 50, 51, 52, and 53, are mounted. Each suspension arm is typically mounted at a small angle (e.g., 2.degree.) with respect to its respective horizontal positioning arm 40, 41 and 42 such that the suspension arm, e.g., 40a, and transducer head, e.g., 50, lie in a plane that intersects the horizontal at angle a. Positioning arm 41 is mounted in the space between disks 10 and 11 and is provided with two angularly mounted head suspension assemblies (41a, 51 and 41b, 52). Head 51 is adapted to read and write information on the bottom surface 10b of disk 10 and head 52 is adapted to read and write information on the top surface 11a of disk 11 in a manner that is well known in the art. The disks and positioning arms are mounted within a sealed housing such as that shown at 4 in FIG. 1A.
It is common for the suspension assemblies to be arranged such that the heads initially lie on their respective disk surfaces. As is well known in the art, the disks are rotated about longitudinal axis I--I by a spindle motor and such rotation induces air flow over the disk. The air flow causes the head slider assemblies to aerodynamically fly over the surface of the disk. Rotation of the actuator moves the positioning arm and head suspension assembly over various concentric data tracks located on the disk for reading and writing data or servo information.
FIG. 2 is an enlarged geometrical representation of a suspension arm 40a showing how pivotal motion of positioning arm 40 through a given vertical distance produces horizontal motion causing undesirable cross track motion of the head and hence off-track error. FIG. 2 demonstrates that this effect is more pronounced, i.e., greater horizontal or cross track motion is produced, when using an angled suspension arm.
Line oc represents a greatly enlarged suspension arm 40a mounted at a 0.degree. angle with respect to the positioning arm 40 (line bo) which is aligned with the horizontal. Vibration of positioning arm 40 results in pivotal movement of the arm about the point from which it is suspended (i.e., point b in FIG. 1) in the plane of the paper. A head mounted at point c will move along an arc when subjected to air turbulence. Assuming a given amount of angular deflection x, the head at point c will vibrate between positions indicated by dashed lines bo.sub.o c.sub.o and bo.sub.1 c.sub.1. Movement of the arm along the arc produces a corresponding change in both the vertical and horizontal positions of the head located at point c as indicated by v and h, respectively. When the arm 40a is mounted at a 0.degree. angle with respect to positioning arm 40, the horizontal component h of the vibratory motion will be infinitesimal for a given angular deflection x.
However, as the angle at which the suspension arm is connected relative to the horizontal positioning arm increases either below (as shown in FIG. 2) or above the horizontal, the horizontal component of the pivotal vibratory motion increases to amounts which result in significant off-track error when positioning a head over a disk track.
For example, if the arm 40a is mounted at an angle a with respect to the positioning arm 40 as shown in FIG. 2 and undergoes the same amount of vibratory angular deflection x, the arm assembly 40, 40a will vibrate between positions bo.sub.o c and bo.sub.1 c.sub.2. The resulting change in vertical position is v.sub.1, and the change in horizontal position is hl which is much greater than h. For a positioning arm having a length of 3.75 inches, a suspension arm length of 1 inch and a suspension angle of 2.degree. with respect to the positioning arm, a vibration producing a change in vertical position vl of 0.001 inches results in a change in horizontal position hl of approximately 40 micro inches. At high track densities such as those greater than 1500 tpi, 40 micro inches is a significant amount of cross track motion to cause intolerable off-track errors, i.e., the transducer head would not occupy the desired position for reading or writing information from a particular sector of a track.
As shown in FIG. 2, the head of suspended arm assembly 40, 40a (line boc.sub.1) is located at point c.sub.1, such that it is directly over data sector P1 of track 2 of the disk 10. Vibratory motion of the head between points c and c.sub.2 causes movement of the head through the horizontal distance h.sub.1. This results in inaccurate positioning as the head vibrates between data sector P.sub.2 of track 1 and data sector P of track 3 instead of being located over the desired sector P.sub.1 of track 2.
Experimentation has shown that the positioning arm may undergo vertical vibrations on the order of 275 Hz. The vibration amplitude decreases as the head assembly moves toward the center of rotation of the disk and increases at the outer disk edge. Applicants have discovered that air turbulence at the disk edge is the major cause of the vibration. At track densities greater than 1500 tpi, such vibration causes significant off-track motion. Whether this vibratory cross track motion actually causes the head to occupy positions between points on two different data tracks or between a point on the desired data track on another point located in between data tracks depends on the track density of the particular disk used. In either case inaccurate positioning results.
Inaccuracy of head positioning is also a problem at track densities less than 1500 tpi when positioning arms of reduced weight and hence, reduced stiffness, are employed.